A position anchor sinks the double-drift illusion.

Area of Science:

• Visual perception
• Computational neuroscience
• Psychophysics

Background:

• The double-drift illusion demonstrates a dramatic shift in perceived motion path when a Gabor patch's internal texture moves orthogonally to its envelope's motion.
• This illusion is particularly pronounced in peripheral vision, affecting both perceived position and direction relative to the actual path.

Purpose of the Study:

• To investigate the role of positional uncertainty in the double-drift illusion.
• To determine if manipulating positional certainty can modulate the magnitude of the illusory shift.

Main Methods:

• Participants viewed a Gabor patch undergoing the double-drift illusion.
• An anchoring line was presented at varying distances from the Gabor's path to assess its effect on perceived location.
• Crowding techniques were used to degrade the positional information of the anchoring line.

Main Results:

• An anchoring line placed close to the Gabor patch significantly reduced the magnitude of the illusory position shift by approximately 50%.
• This suppressive effect of the anchor was symmetrical, regardless of whether it was placed on either side of the Gabor.
• When the anchoring line's position information was degraded by crowding, the illusory shift was largely restored, indicating the importance of positional certainty.

Conclusions:

• Positional uncertainty of the Gabor patch is a critical factor driving the illusory position offset observed in the double-drift illusion.
• The ability of an external anchor to suppress the illusion is dependent on the certainty of its own positional information.
• These findings highlight the interplay between local stimulus properties and contextual information in shaping visual perception.